This invention relates to a printed circuit board base material, and provides a novel printed circuit board base material which allows a high signal transmission speed.
Printed circuit boards are widely used in electronic devices in the place of complicated connections and distributions of conductors. Most conventional printed circuit boards are generally formed by directly depositing conductors, i.e., components of electrical circuits, on epoxy base materials, glass-epoxy base materials, or ceramic base materials, for example.
Some other conventional printed circuit boards are formed by directly depositing the same conductors as mentioned above on flexible base materials made of polyimide resin sheets or polyester resin sheets, for example.
Recently, such high speed elements as gallium arsenide IC's have been developed. As a result, increasing transmission speed has been set as a goal for the printed circuit boards of the classes described above. Delay in the propagation time is affected by the dielectric constant of the base material used for the board. Thus, the material of the board is required to possess a low dielectric constant to permit an increase of the operating speed of the device. The conventional printed circuit boards mentioned above have fairly large dielectric constants falling on the order of 4 to 7 (at 1 MHz), and are not presently capable of satisfactorily meeting the increased speed requirements.
U.S. Pat. No. 4,379,858 discloses a melt molded foamed plastic composition of a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer resin matrix having expanded, porous polytetrafluoroethylene fragments mixed therein.
U.S. Pat. No. 4,454,249 discloses reinforced plastic compositions which comprise a fluoroplastic resin matrix selected from the group consisting of polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, polytrifluorochloroethylene and polyvinylidene fluoride, and stretched, porous polytetrafluoroethylene resin fragments mixed thereinto.
U.S. Pat. No. 4,640,866 discloses a printed circuit board comprising at least one layer of metal firmly bonded in laminar contact with at least one layer of solid, sintered polytetrafluoroethylene (PTFE). In one embodiment, the solid PTFE layer contains fibers of porous, expanded, sintered PTFE mixed within it. In another embodiment, the solid PTFE layer is firmly bonded to the metal layer on one side and is firmly bonded on the other side to a layer of porous, expanded, sintered PTFE.